Drills are commonly used in woodworking. They are also used for cutting holes in such materials as composite materials (e.g. composites of wood and plastic), plastics such as polypropylene and polyvinyl acetate, woods, metals, especially softer metals such as iron and the like. The drill is a tool with a rotary drill bit used to drill holes through such materials. The twist drill is the most commonly used drill, and comprises a drill bit in the form of a cylindrical metal rod with two helical “flutes” or grooves spiraling along its length. The drill bit is typically held by the drill at one end, in the “chuck”, with the other end (i.e. the working end) available for drilling the workpiece when the drill bit is rotated. The working tip of the drill bit cuts into the workpiece, slicing off debris in the form of thin shavings or small particles. The debris is carried up and away from the tip via the helical flutes or grooves once it has been lifted clear of the drilling hole.
It is often desirable to drill or bore holes in a workpiece to enable connecting or fastening devices such as screws, bolts and the like to be easily inserted in the workpiece. This predrilling process reduces the force necessary to properly seat the fastening device in the workpiece and at least substantially reduces breakage of the fastening device and/or damage to the workpiece. This is especially of concern when inserting countersink fastening devices into the workpiece where the force needed for the countersink head to enter the workpiece significantly exceeds the force needed to insert the body of the fastening device into the workpiece. This sudden, sharp increase in torque can result in damage or breakage of the fastening device. For example, fastening devices which are drilled directly into the work piece can cause splitting or splintering of the workpiece at the surface of the workpiece. Even when successfully inserted without predrilling, the fastening device may cause the workpiece to split, requiring the workpiece to be replaced. Another common problem without predrilling is splintering, which leaves an unsightly appearance that can only be remedied by sanding and the like. Also, if the workpiece is made out of either plastic or plastic/wood composite, predrilling can prevent the waste from gathering at the top of the waste piece in unsightly small mounds, commonly referred to as surface “volcanoes”.
It is desirable to pre-drill the holes to a precise depth corresponding to the depth of the fastening device when precisely seated within the workpiece so that the top or head of the fastening device is even with the surface of the workpiece. Accordingly, it is desirable to provide devices that accurately limit the depth of the drilling hole to provide precise seating of the fastening device within the workpiece. Devices for limiting the depth of a drilling tool have been used to provide more precise drilling performance and typically include a body that is removably attached to the drilling tool, for example, by a set screw extending through the body. The device may be secured to the drilling tool at a select position, which defines the depth of the drilling hole by limiting the forward penetration of the drilling tool into the workpiece.
Once the depth limiting device comes into contact with the workpiece, the drilling tool is prevented from penetrating further into the workpiece because the depth limiting device acts as a barrier against further penetration. Because the depth limiting device is typically affixed to the drilling tool so that it cannot rotate independently with respect thereto, the depth limiting device continues to rotate with the drilling tool when it comes into contact with the workpiece. The driving frictional contact between the depth limiting device and the workpiece can cause marring or other damage to the workpiece.
Depth limiting devices for drilling tools having rotatable contact structures are also known in the art. The contact structures rotate with the drilling tool (i.e., drill bit) thereby generating frictional contact between the depth limiting device and the workpiece. During operation, as the rotatable contact structure comes into contact with the workpiece, marring of the workpiece results since the stoppage of rotation is not immediate and significant frictional contact is applied to the workpiece. The rotatable contact structure possesses rotational momentum which generates a level of frictional contact that cannot be immediately eliminated when the depth limiting device comes into contact with workpiece. This can result in some damage to the workpiece, and to the contact surface of the depth limiting device itself.
Depth limiting devices must also precisely limit the depth of the drilling hole. However, during drilling or boring, debris is generated from the workpiece, which can interface with the surface of the workpiece thereby increasing the possibility of an inaccurate drill hole. In particular, the presence of debris can prevent all or a portion of the contact surface of the depth limiting device from contacting the surface of the workpiece, thus causing the depth of the hole to be inaccurate. Moreover, the contact structures can adversely interact with the debris present at the interface of the depth limiting device and the workpiece in a manner that can mar or damage the surface of the workpiece.
Accordingly, there is a need for a depth limiting device for use with a hole forming apparatus such as a drilling or boring tool that is designed to drill or bore a hole to a desired precise depth, while effectively protecting the surface of the workpiece from marring or other damage. There is a further need for a depth limiting device that minimizes the presence of debris on the surface of the workpiece, thus facilitating precise drilling and easy clean up. Furthermore, there is a need for a depth limiting device that is simple and cost efficient to make and use.